This application is based upon Japanese Patent Application No. Hei 3-230127 on which priority is claimed, a disclosure of which is incorporated by reference.
The present invention relates to a zooming viewfinder that is primarily intended to be used with compact cameras.
An example of the prior art zooming viewfinders for use with compact cameras is shown schematically in FIG. 14.
The viewfinder shown in FIG. 14 comprises, in order from the object side, a biconvex first lens 1, a second and third lens 2 and 3 which are each a negative meniscus lens, and a positive fourth and a fifth lens 4 and 5 which compose an eyepiece. The surface on the pupil side of the third lens 3 is a half mirror surface m and a field-limiting frame f is depicted on the object side of the fourth lens 4. The field-limiting frame f on the fourth lens 4 is illuminated with incoming rays of light from the object and the light reflected by the half mirror surface m travels through the eyepiece to be incident on the pupil of the viewer (not shown).
Referring to FIG. 14, a light beam L1 intercepting the first lens group 1 at height H' passes through the pupil P at a position of height HL, whereas a light beam L2 indicated by a one-dot-and-dash line passes through the pupil P at a position of height HU.
However, with the prior art zooming viewfinder described above, the lens diameter of the first lens group on the object side has to be made large for two reasons: the first reason is that the pupil is located in a rear position; secondly, it is necessary to insure that the light reflected from the field-limiting frame illuminated by the brightness of the object will not undergo vignetting at the position of the pupil.
If the diameter of the first lens group is small, a light beam L3 that intercepts the first lens group at height H and which is indicated by a dashed line will pass through the pupil P at a position lower than HL as also indicated by a dashed line and, as a result, the illumination falling on the viewfinder or the field-limiting frame becomes deficient.